**
 	* Copyright (c) 2010 The Chromium Authors. All rights reserved. Use of this
 	* source code is governed by a BSD-style license that can be found in the
 	* LICENSE file.
 	*/
 	
 	/**
 	* Constructor - no need to invoke directly, call initBackgroundPage instead.
 	* @constructor
 	* @param {String} url_request_token The OAuth request token URL.
 	* @param {String} url_auth_token The OAuth authorize token URL.
 	* @param {String} url_access_token The OAuth access token URL.
 	* @param {String} consumer_key The OAuth consumer key.
 	* @param {String} consumer_secret The OAuth consumer secret.
 	* @param {String} oauth_scope The OAuth scope parameter.
 	* @param {Object} opt_args Optional arguments. Recognized parameters:
 	* "app_name" {String} Name of the current application
 	* "callback_page" {String} If you renamed chrome_ex_oauth.html, the name
 	* this file was renamed to.
 	*/
 	function ChromeExOAuth(url_request_token, url_auth_token, url_access_token,
 	consumer_key, consumer_secret, oauth_scope, opt_args) {
 	this.url_request_token = url_request_token;
 	this.url_auth_token = url_auth_token;
 	this.url_access_token = url_access_token;
 	this.consumer_key = consumer_key;
 	this.consumer_secret = consumer_secret;
 	this.oauth_scope = oauth_scope;
 	this.app_name = opt_args && opt_args['app_name'] ||
 	"ChromeExOAuth Library";
 	this.key_token = "oauth_token";
 	this.key_token_secret = "oauth_token_secret";
 	this.callback_page = opt_args && opt_args['callback_page'] ||
 	"chrome_ex_oauth.html";
 	this.auth_params = {};
 	if (opt_args && opt_args['auth_params']) {
 	for (key in opt_args['auth_params']) {
 	if (opt_args['auth_params'].hasOwnProperty(key)) {
 	this.auth_params[key] = opt_args['auth_params'][key];
 	}
 	}
 	}
 	};
 	
 	/*******************************************************************************
 	* PUBLIC API METHODS
 	* Call these from your background page.
 	******************************************************************************/
 	
 	/**
 	* Initializes the OAuth helper from the background page. You must call this
 	* before attempting to make any OAuth calls.
 	* @param {Object} oauth_config Configuration parameters in a JavaScript object.
 	* The following parameters are recognized:
 	* "request_url" {String} OAuth request token URL.
 	* "authorize_url" {String} OAuth authorize token URL.
 	* "access_url" {String} OAuth access token URL.
 	* "consumer_key" {String} OAuth consumer key.
 	* "consumer_secret" {String} OAuth consumer secret.
 	* "scope" {String} OAuth access scope.
 	* "app_name" {String} Application name.
 	* "auth_params" {Object} Additional parameters to pass to the
 	* Authorization token URL. For an example, 'hd', 'hl', 'btmpl':
 	* http://code.google.com/apis/accounts/docs/OAuth_ref.html#GetAuth
 	* @return {ChromeExOAuth} An initialized ChromeExOAuth object.
 	*/
 	ChromeExOAuth.initBackgroundPage = function(oauth_config) {
 	window.chromeExOAuthConfig = oauth_config;
 	window.chromeExOAuth = ChromeExOAuth.fromConfig(oauth_config);
 	window.chromeExOAuthRedirectStarted = false;
 	window.chromeExOAuthRequestingAccess = false;
 	
 	var url_match = chrome.extension.getURL(window.chromeExOAuth.callback_page);
 	var tabs = {};
 	chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab) {
 	if (changeInfo.url &&
 	changeInfo.url.substr(0, url_match.length) === url_match &&
 	changeInfo.url != tabs[tabId] &&
 	window.chromeExOAuthRequestingAccess == false) {
 	chrome.tabs.create({ 'url' : changeInfo.url }, function(tab) {
 	tabs[tab.id] = tab.url;
 	chrome.tabs.remove(tabId);
 	});
 	}
 	});
 	
 	return window.chromeExOAuth;
 	};
 	
 	/**
 	* Authorizes the current user with the configued API. You must call this
 	* before calling sendSignedRequest.
 	* @param {Function} callback A function to call once an access token has
 	* been obtained. This callback will be passed the following arguments:
 	* token {String} The OAuth access token.
 	* secret {String} The OAuth access token secret.
 	*/
 	ChromeExOAuth.prototype.authorize = function(callback) {
 	if (this.hasToken()) {
 	callback(this.getToken(), this.getTokenSecret());
 	} else {
 	window.chromeExOAuthOnAuthorize = function(token, secret) {
 	callback(token, secret);
 	};
 	chrome.tabs.create({ 'url' :chrome.extension.getURL(this.callback_page) });
 	}
 	};
 	
 	/**
 	* Clears any OAuth tokens stored for this configuration. Effectively a
 	* "logout" of the configured OAuth API.
 	*/
 	ChromeExOAuth.prototype.clearTokens = function() {
 	delete localStorage[this.key_token + encodeURI(this.oauth_scope)];
 	delete localStorage[this.key_token_secret + encodeURI(this.oauth_scope)];
 	};
 	
 	/**
 	* Returns whether a token is currently stored for this configuration.
 	* Effectively a check to see whether the current user is "logged in" to
 	* the configured OAuth API.
 	* @return {Boolean} True if an access token exists.
 	*/
 	ChromeExOAuth.prototype.hasToken = function() {
 	return !!this.getToken();
 	};
 	
 	/**
 	* Makes an OAuth-signed HTTP request with the currently authorized tokens.
 	* @param {String} url The URL to send the request to. Querystring parameters
 	* should be omitted.
 	* @param {Function} callback A function to be called once the request is
 	* completed. This callback will be passed the following arguments:
 	* responseText {String} The text response.
 	* xhr {XMLHttpRequest} The XMLHttpRequest object which was used to
 	* send the request. Useful if you need to check response status
 	* code, etc.
 	* @param {Object} opt_params Additional parameters to configure the request.
 	* The following parameters are accepted:
 	* "method" {String} The HTTP method to use. Defaults to "GET".
 	* "body" {String} A request body to send. Defaults to null.
 	* "parameters" {Object} Query parameters to include in the request.
 	* "headers" {Object} Additional headers to include in the request.
 	*/
 	ChromeExOAuth.prototype.sendSignedRequest = function(url, callback,
 	opt_params) {
 	var method = opt_params && opt_params['method'] || 'GET';
 	var body = opt_params && opt_params['body'] || null;
 	var params = opt_params && opt_params['parameters'] || {};
 	var headers = opt_params && opt_params['headers'] || {};
 	
 	var signedUrl = this.signURL(url, method, params);
 	
 	ChromeExOAuth.sendRequest(method, signedUrl, headers, body, function (xhr) {
 	if (xhr.readyState == 4) {
 	callback(xhr.responseText, xhr);
 	}
 	});
 	};
 	
 	/**
 	* Adds the required OAuth parameters to the given url and returns the
 	* result. Useful if you need a signed url but don't want to make an XHR
 	* request.
 	* @param {String} method The http method to use.
 	* @param {String} url The base url of the resource you are querying.
 	* @param {Object} opt_params Query parameters to include in the request.
 	* @return {String} The base url plus any query params plus any OAuth params.
 	*/
 	ChromeExOAuth.prototype.signURL = function(url, method, opt_params) {
 	var token = this.getToken();
 	var secret = this.getTokenSecret();
 	if (!token || !secret) {
 	throw new Error("No oauth token or token secret");
 	}
 	
 	var params = opt_params || {};
 	
 	var result = OAuthSimple().sign({
 	action : method,
 	path : url,
 	parameters : params,
 	signatures: {
 	consumer_key : this.consumer_key,
 	shared_secret : this.consumer_secret,
 	oauth_secret : secret,
 	oauth_token: token
 	}
 	});
 	
 	return result.signed_url;
 	};
 	
 	/**
 	* Generates the Authorization header based on the oauth parameters.
 	* @param {String} url The base url of the resource you are querying.
 	* @param {Object} opt_params Query parameters to include in the request.
 	* @return {String} An Authorization header containing the oauth_* params.
 	*/
 	ChromeExOAuth.prototype.getAuthorizationHeader = function(url, method,
 	opt_params) {
 	var token = this.getToken();
 	var secret = this.getTokenSecret();
 	if (!token || !secret) {
 	throw new Error("No oauth token or token secret");
 	}
 	
 	var params = opt_params || {};
 	
 	return OAuthSimple().getHeaderString({
 	action: method,
 	path : url,
 	parameters : params,
 	signatures: {
 	consumer_key : this.consumer_key,
 	shared_secret : this.consumer_secret,
 	oauth_secret : secret,
 	oauth_token: token
 	}
 	});
 	};
 	
 	/*******************************************************************************
 	* PRIVATE API METHODS
 	* Used by the library. There should be no need to call these methods directly.
 	******************************************************************************/
 	
 	/**
 	* Creates a new ChromeExOAuth object from the supplied configuration object.
 	* @param {Object} oauth_config Configuration parameters in a JavaScript object.
 	* The following parameters are recognized:
 	* "request_url" {String} OAuth request token URL.
 	* "authorize_url" {String} OAuth authorize token URL.
 	* "access_url" {String} OAuth access token URL.
 	* "consumer_key" {String} OAuth consumer key.
 	* "consumer_secret" {String} OAuth consumer secret.
 	* "scope" {String} OAuth access scope.
 	* "app_name" {String} Application name.
 	* "auth_params" {Object} Additional parameters to pass to the
 	* Authorization token URL. For an example, 'hd', 'hl', 'btmpl':
 	* http://code.google.com/apis/accounts/docs/OAuth_ref.html#GetAuth
 	* @return {ChromeExOAuth} An initialized ChromeExOAuth object.
 	*/
 	ChromeExOAuth.fromConfig = function(oauth_config) {
 	return new ChromeExOAuth(
 	oauth_config['request_url'],
 	oauth_config['authorize_url'],
 	oauth_config['access_url'],
 	oauth_config['consumer_key'],
 	oauth_config['consumer_secret'],
 	oauth_config['scope'],
 	{
 	'app_name' : oauth_config['app_name'],
 	'auth_params' : oauth_config['auth_params']
 	}
 	);
 	};
 	
 	/**
 	* Initializes chrome_ex_oauth.html and redirects the page if needed to start
 	* the OAuth flow. Once an access token is obtained, this function closes
 	* chrome_ex_oauth.html.
 	*/
 	ChromeExOAuth.initCallbackPage = function() {
 	var background_page = chrome.extension.getBackgroundPage();
 	var oauth_config = background_page.chromeExOAuthConfig;
 	var oauth = ChromeExOAuth.fromConfig(oauth_config);
 	background_page.chromeExOAuthRedirectStarted = true;
 	oauth.initOAuthFlow(function (token, secret) {
 	background_page.chromeExOAuthOnAuthorize(token, secret);
 	background_page.chromeExOAuthRedirectStarted = false;
 	chrome.tabs.getSelected(null, function (tab) {
 	chrome.tabs.remove(tab.id);
 	});
 	});
 	};
 	
 	/**
 	* Sends an HTTP request. Convenience wrapper for XMLHttpRequest calls.
 	* @param {String} method The HTTP method to use.
 	* @param {String} url The URL to send the request to.
 	* @param {Object} headers Optional request headers in key/value format.
 	* @param {String} body Optional body content.
 	* @param {Function} callback Function to call when the XMLHttpRequest's
 	* ready state changes. See documentation for XMLHttpRequest's
 	* onreadystatechange handler for more information.
 	*/
 	ChromeExOAuth.sendRequest = function(method, url, headers, body, callback) {
 	var xhr = new XMLHttpRequest();
 	xhr.onreadystatechange = function(data) {
 	callback(xhr, data);
 	}
 	xhr.open(method, url, true);
 	if (headers) {
 	for (var header in headers) {
 	if (headers.hasOwnProperty(header)) {
 	xhr.setRequestHeader(header, headers[header]);
 	}
 	}
 	}
 	xhr.send(body);
 	};
 	
 	/**
 	* Decodes a URL-encoded string into key/value pairs.
 	* @param {String} encoded An URL-encoded string.
 	* @return {Object} An object representing the decoded key/value pairs found
 	* in the encoded string.
 	*/
 	ChromeExOAuth.formDecode = function(encoded) {
 	var params = encoded.split("&");
 	var decoded = {};
 	for (var i = 0, param; param = params[i]; i++) {
 	var keyval = param.split("=");
 	if (keyval.length == 2) {
 	var key = ChromeExOAuth.fromRfc3986(keyval[0]);
 	var val = ChromeExOAuth.fromRfc3986(keyval[1]);
 	decoded[key] = val;
 	}
 	}
 	return decoded;
 	};
 	
 	/**
 	* Returns the current window's querystring decoded into key/value pairs.
 	* @return {Object} A object representing any key/value pairs found in the
 	* current window's querystring.
 	*/
 	ChromeExOAuth.getQueryStringParams = function() {
 	var urlparts = window.location.href.split("?");
 	if (urlparts.length >= 2) {
 	var querystring = urlparts.slice(1).join("?");
 	return ChromeExOAuth.formDecode(querystring);
 	}
 	return {};
 	};
 	
 	/**
 	* Binds a function call to a specific object. This function will also take
 	* a variable number of additional arguments which will be prepended to the
 	* arguments passed to the bound function when it is called.
 	* @param {Function} func The function to bind.
 	* @param {Object} obj The object to bind to the function's "this".
 	* @return {Function} A closure that will call the bound function.
 	*/
 	ChromeExOAuth.bind = function(func, obj) {
 	var newargs = Array.prototype.slice.call(arguments).slice(2);
 	return function() {
 	var combinedargs = newargs.concat(Array.prototype.slice.call(arguments));
 	func.apply(obj, combinedargs);
 	};
 	};
 	
 	/**
 	* Encodes a value according to the RFC3986 specification.
 	* @param {String} val The string to encode.
 	*/
 	ChromeExOAuth.toRfc3986 = function(val){
 	return encodeURIComponent(val)
 	.replace(/\!/g, "%21")
 	.replace(/\*/g, "%2A")
 	.replace(/'/g, "%27")
 	.replace(/\(/g, "%28")
 	.replace(/\)/g, "%29");
 	};
 	
 	/**
 	* Decodes a string that has been encoded according to RFC3986.
 	* @param {String} val The string to decode.
 	*/
 	ChromeExOAuth.fromRfc3986 = function(val){
 	var tmp = val
 	.replace(/%21/g, "!")
 	.replace(/%2A/g, "*")
 	.replace(/%27/g, "'")
 	.replace(/%28/g, "(")
 	.replace(/%29/g, ")");
 	return decodeURIComponent(tmp);
 	};
 	
 	/**
 	* Adds a key/value parameter to the supplied URL.
 	* @param {String} url An URL which may or may not contain querystring values.
 	* @param {String} key A key
 	* @param {String} value A value
 	* @return {String} The URL with URL-encoded versions of the key and value
 	* appended, prefixing them with "&" or "?" as needed.
 	*/
 	ChromeExOAuth.addURLParam = function(url, key, value) {
 	var sep = (url.indexOf('?') >= 0) ? "&" : "?";
 	return url + sep +
 	ChromeExOAuth.toRfc3986(key) + "=" + ChromeExOAuth.toRfc3986(value);
 	};
 	
 	/**
 	* Stores an OAuth token for the configured scope.
 	* @param {String} token The token to store.
 	*/
 	ChromeExOAuth.prototype.setToken = function(token) {
 	localStorage[this.key_token + encodeURI(this.oauth_scope)] = token;
 	};
 	
 	/**
 	* Retrieves any stored token for the configured scope.
 	* @return {String} The stored token.
 	*/
 	ChromeExOAuth.prototype.getToken = function() {
 	return localStorage[this.key_token + encodeURI(this.oauth_scope)];
 	};
 	
 	/**
 	* Stores an OAuth token secret for the configured scope.
 	* @param {String} secret The secret to store.
 	*/
 	ChromeExOAuth.prototype.setTokenSecret = function(secret) {
 	localStorage[this.key_token_secret + encodeURI(this.oauth_scope)] = secret;
 	};
 	
 	/**
 	* Retrieves any stored secret for the configured scope.
 	* @return {String} The stored secret.
 	*/
 	ChromeExOAuth.prototype.getTokenSecret = function() {
 	return localStorage[this.key_token_secret + encodeURI(this.oauth_scope)];
 	};
 	
 	/**
 	* Starts an OAuth authorization flow for the current page. If a token exists,
 	* no redirect is needed and the supplied callback is called immediately.
 	* If this method detects that a redirect has finished, it grabs the
 	* appropriate OAuth parameters from the URL and attempts to retrieve an
 	* access token. If no token exists and no redirect has happened, then
 	* an access token is requested and the page is ultimately redirected.
 	* @param {Function} callback The function to call once the flow has finished.
 	* This callback will be passed the following arguments:
 	* token {String} The OAuth access token.
 	* secret {String} The OAuth access token secret.
 	*/
 	ChromeExOAuth.prototype.initOAuthFlow = function(callback) {
 	if (!this.hasToken()) {
 	var params = ChromeExOAuth.getQueryStringParams();
 	if (params['chromeexoauthcallback'] == 'true') {
 	var oauth_token = params['oauth_token'];
 	var oauth_verifier = params['oauth_verifier']
 	this.getAccessToken(oauth_token, oauth_verifier, callback);
 	} else {
 	var request_params = {
 	'url_callback_param' : 'chromeexoauthcallback'
 	}
 	this.getRequestToken(function(url) {
 	window.location.href = url;
 	}, request_params);
 	}
 	} else {
 	callback(this.getToken(), this.getTokenSecret());
 	}
 	};
 	
 	/**
 	* Requests an OAuth request token.
 	* @param {Function} callback Function to call once the authorize URL is
 	* calculated. This callback will be passed the following arguments:
 	* url {String} The URL the user must be redirected to in order to
 	* approve the token.
 	* @param {Object} opt_args Optional arguments. The following parameters
 	* are accepted:
 	* "url_callback" {String} The URL the OAuth provider will redirect to.
 	* "url_callback_param" {String} A parameter to include in the callback
 	* URL in order to indicate to this library that a redirect has
 	* taken place.
 	*/
 	ChromeExOAuth.prototype.getRequestToken = function(callback, opt_args) {
 	if (typeof callback !== "function") {
 	throw new Error("Specified callback must be a function.");
 	}
 	var url = opt_args && opt_args['url_callback'] ||
 	window && window.top && window.top.location &&
 	window.top.location.href;
 	
 	var url_param = opt_args && opt_args['url_callback_param'] ||
 	"chromeexoauthcallback";
 	var url_callback = ChromeExOAuth.addURLParam(url, url_param, "true");
 	
 	var result = OAuthSimple().sign({
 	path : this.url_request_token,
 	parameters: {
 	"xoauth_displayname" : this.app_name,
 	"scope" : this.oauth_scope,
 	"oauth_callback" : url_callback
 	},
 	signatures: {
 	consumer_key : this.consumer_key,
 	shared_secret : this.consumer_secret
 	}
 	});
 	var onToken = ChromeExOAuth.bind(this.onRequestToken, this, callback);
 	ChromeExOAuth.sendRequest("GET", result.signed_url, null, null, onToken);
 	};
 	
 	/**
 	* Called when a request token has been returned. Stores the request token
 	* secret for later use and sends the authorization url to the supplied
 	* callback (for redirecting the user).
 	* @param {Function} callback Function to call once the authorize URL is
 	* calculated. This callback will be passed the following arguments:
 	* url {String} The URL the user must be redirected to in order to
 	* approve the token.
 	* @param {XMLHttpRequest} xhr The XMLHttpRequest object used to fetch the
 	* request token.
 	*/
 	ChromeExOAuth.prototype.onRequestToken = function(callback, xhr) {
 	if (xhr.readyState == 4) {
 	if (xhr.status == 200) {
 	var params = ChromeExOAuth.formDecode(xhr.responseText);
 	var token = params['oauth_token'];
 	this.setTokenSecret(params['oauth_token_secret']);
 	var url = ChromeExOAuth.addURLParam(this.url_auth_token,
 	"oauth_token", token);
 	for (var key in this.auth_params) {
 	if (this.auth_params.hasOwnProperty(key)) {
 	url = ChromeExOAuth.addURLParam(url, key, this.auth_params[key]);
 	}
 	}
 	callback(url);
 	} else {
 	throw new Error("Fetching request token failed. Status " + xhr.status);
 	}
 	}
 	};
 	
 	/**
 	* Requests an OAuth access token.
 	* @param {String} oauth_token The OAuth request token.
 	* @param {String} oauth_verifier The OAuth token verifier.
 	* @param {Function} callback The function to call once the token is obtained.
 	* This callback will be passed the following arguments:
 	* token {String} The OAuth access token.
 	* secret {String} The OAuth access token secret.
 	*/
 	ChromeExOAuth.prototype.getAccessToken = function(oauth_token, oauth_verifier,
 	callback) {
 	if (typeof callback !== "function") {
 	throw new Error("Specified callback must be a function.");
 	}
 	var bg = chrome.extension.getBackgroundPage();
 	if (bg.chromeExOAuthRequestingAccess == false) {
 	bg.chromeExOAuthRequestingAccess = true;
 	
 	var result = OAuthSimple().sign({
 	path : this.url_access_token,
 	parameters: {
 	"oauth_token" : oauth_token,
 	"oauth_verifier" : oauth_verifier
 	},
 	signatures: {
 	consumer_key : this.consumer_key,
 	shared_secret : this.consumer_secret,
 	oauth_secret : this.getTokenSecret(this.oauth_scope)
 	}
 	});
 	
 	var onToken = ChromeExOAuth.bind(this.onAccessToken, this, callback);
 	ChromeExOAuth.sendRequest("GET", result.signed_url, null, null, onToken);
 	}
 	};
 	
 	/**
 	* Called when an access token has been returned. Stores the access token and
 	* access token secret for later use and sends them to the supplied callback.
 	* @param {Function} callback The function to call once the token is obtained.
 	* This callback will be passed the following arguments:
 	* token {String} The OAuth access token.
 	* secret {String} The OAuth access token secret.
 	* @param {XMLHttpRequest} xhr The XMLHttpRequest object used to fetch the
 	* access token.
 	*/
 	ChromeExOAuth.prototype.onAccessToken = function(callback, xhr) {
 	if (xhr.readyState == 4) {
 	var bg = chrome.extension.getBackgroundPage();
 	if (xhr.status == 200) {
 	var params = ChromeExOAuth.formDecode(xhr.responseText);
 	var token = params["oauth_token"];
 	var secret = params["oauth_token_secret"];
 	this.setToken(token);
 	this.setTokenSecret(secret);
 	bg.chromeExOAuthRequestingAccess = false;
 	callback(token, secret);
 	} else {
 	bg.chromeExOAuthRequestingAccess = false;
 	throw new Error("Fetching access token failed with status " + xhr.status);
 	}
 	}
 	};